Some important factors in a preterm infant's ability to respond to respiratory disease are surfactant deficiency, inefficient thoracic cage, highly compliant chest wall, and fatiguability of respiratory muscles. Surfactant deficiency has been greatly reduced by the introduction of surfactant replacement therapy. The purpose of this study is to determine if respiratory training can increase muscle endurance and strength in preterm infants by decreasing chest wall distortion thereby increasing respiratory mechanical efficiency.